A US woman who shot and killed her husband and two adult children before taking her own life is thought to have committed the shocking crime as a result of being ostracised from the religion she was raised in.

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Her parents, John and Patsy Ramsey, and brother Burke, who was nine at the time of the killing, have at various times been considered suspects.

Katy Perry. (AAP)

As evidence, Johnson says not only do Perry and JonBenét 's faces look similar, but Perry's parents, pastors Keith Hudson and Mary Perry, bare a resemblance to Ramsey's parents, Patsy and John Bennett Ramsey.

Patsy Ramsey died of cancer in 2006.

The video has been viewed more than 315,000 times.

In other conspiracy news, a Florida poll has revealed almost 40 percent of voters believe Republican presidential candidate Ted Cruz could in fact be the Zodiac killer, who is thought to have murdered between five and 37 people across California during the 1960s and 1970s.